1. Field
The present disclosure relates to rectifying antennas (“rectennas”), and more, particularly to a rectenna array for harvesting radio frequency (“RF”) energy.
2. Related Art
Rectennas are known in the art. A rectenna is a rectifying antenna, which is a type of antenna that is utilized to convert ambient electromagnetic energy that impinges on the rectenna into direct current (“DC”) electricity. An example of a simple rectenna element includes a dipole antenna with a radio frequency (“RF”) diode connected across the dipole antenna terminals. In an example of operation, the dipole antenna receives the ambient electromagnetic energy that impinges on the dipole antenna. The ambient electromagnetic energy then induces an alternating current (“AC current”) on the dipole antenna that is passed to the RF diode. The RF diode then rectifies the AC current induced on the dipole antenna to produce a DC current. The DC current then powers a load connected across the RF diode terminals. In general, an example of an RF diode for a rectenna is a Schottky diode because Schottky diodes have low voltage drops and high speed electrical characteristics that result in low power losses due to the conduction of the AC and DC currents and the switching of the diode.
Commercially available diodes such as, for example, P-N junction, PIN, and Schottky diodes all have turn-on voltages that are higher than 0.30 to 0.40 volts. Unfortunately, these turn-on voltages are too high to convert most of the energy captured by the rectenna in an environment where the impinging ambient electromagnetic energy is low residual, or ultra-low residual, RF energy, which is too low to induce a current capable of producing a voltage that is high enough to turn-on the diode. In this situation, if the power of the impinging ambient electromagnetic energy is too low to produce a voltage that is high enough to turn-on the diode, the captured impinging ambient electromagnetic energy is wasted as heat.
Unfortunately, this results in wasted energy that could be used to power modern near-zero energy consuming (“NZero”) sensors. At present, a number of NZero sensors have been developed for various wireless sensor networks. These NZero sensors monitor various parameters for aerospace vehicles, health monitoring systems, and data collection systems. Additionally, in the example of aerospace vehicles, these NZero sensors may be located in areas of an aerospace vehicle that are either not accessible or not easily accessible. Moreover, the location of these NZero sensors and the total number of NZero sensors (which may be in the thousands) on the aerospace vehicle may be limited by the ability to connect the NZero sensor to physical electrical wires based on both the total weight of the wires and the required wiring paths along the aerospace vehicle, which may be an aircraft or space vehicle. As such, there is a need for a wireless high efficiency RF energy rectifying system capable of operating in residual low or ultra-low residual low RF energy environment.